This invention relates to photopolymerizable epoxide compositions. This invention further relates to extending the useful pot life of epoxide compositions containing a latent, photosensitive catalyst.
The polymerization of epoxides by means of Lewis acids generated by the photoinduced decomposition of specified diazonium salts is taught in U.S. Pat. No. 3,708,296. The patent discloses a large number of diazonium complexes containing precursors of various Lewis acids including phosphorous pentafluoride, antimony pentafluoride, antimony pentachloride and ferric chloride. The diazonium compounds react in the presence of radiation of specific wavelengths in accordance with the following equation: ##STR1##
The result Lewis acid MX.sub.n initiates a polymerization of the epoxide compound. In the foregoing equation M represents a metallic element and X represents fluorine or chlorine.
Certain diazonium complexes disclosed in the aforementioned U.S. Pat. No. 3,708,296 are less than satisfactory in that epoxides containing these catalysts undergo a gradual spontaneous polymerization even when virtually all light is excluded. In some instances this polymerization is sufficiently rapid that the catalyst and epoxide cannot be combined until just prior to exposure of the mixture to the radiation intended to polymerize the epoxide. In many instances it is desirable to store larger quantities of a catalyzed epoxide for extended periods of time which may be as much as several days, to avoid the necessity of blending small quantities as needed. The tendency of some catalysts to decompose prematurely therefore may be a considerable shortcoming.
While it may be possible to stabilize the epoxide-catalyst mixture, by the use of certain additives, these additives may interfere with the desired photoinitiated polymerization in addition to increasing the cost of the formulation.
It is therefore an objective of this invention to provide aryldiazonium complexes of Lewis acids that can be incorporated into epoxide compositions that have considerable pot life in that the mixture of epoxide and catalyst can be kept for extended periods of time prior to being used.
It has now been found that the presence of certain substituents on the phenyl ring of a phenyl diazonium hexafluorophosphate significantly increases the stability of the diazonium compound in the absence of light without substantially affecting the efficacy of the compound as a photoinitiator for the polymerization of epoxides as described in U.S. Pat. No. 3,703,296.